Question

Can phosphorus with outer electronic configuration $3s^{2}3p^3$ form ${PH}_5?$

Answer 1

The ${△}_{H-H}$ of $H_2$ is high & also $H_2$ has slightly negative $△H$ (electron gain enthalpy). Due to this it acts only as a weak oxidising agent.

Although phosphorous exhibit $+3$ & $+5$ oxidation states, the dihydrogen can oxide $p$ to $+3$ oxidation state but not to its highest oxidation state i.e.$+5$. So $P$ forms ${PH}_3$ and not ${PH}_5$.